In reply to dculberson :
That will be it. The fuel pump in the engine will try to pull the tank into a vacuum with the vent closed and low fuel flow is the result.
In reply to dculberson :
That will be it. The fuel pump in the engine will try to pull the tank into a vacuum with the vent closed and low fuel flow is the result.
Haaa... I've done that before. Get about a mile up the lake, the engine dies, and my plastic fuel tank is a pancake.
You'll never get up fully on plane with 10hp with that hull. I would say with one person you'd need closer to 35 hp. What RPM were you spinning? The prop that was shipped with the new 9.9 is likely too much pitch for the boat. They assume it's going on something like a 14' jon boat that weighs 100 lbs, so you may need less pitch to get the RPM you need for full power.
Edit to add: The 4-stroke will be a little more finnicky about RPMs. 2-strokes make power by just whizzing to their peak but they don't make a lot of torque. 4-strokes make more torque, but they also tend to have a bit narrower power band, so if you're not at the RPM they advertise, you'll not make the same speed as a 2-stroke of the same output. This was the cause for so many people claiming that 4-stroke outboards were slower when they first came out, but it was generally because they applied 2-stroke expectations of the powerband. They would slap one on, not pay attention to the RPMs, and get disappointed.
If you don't have a tach, get yourself a cheap Sirometer. Have the son drive at WOT and you can use it on the cowl to see what your RPMs are.
Reading back I saw someone mention keeping water out of the engine. Did you install a fuel/water separator on the fuel line?
I'm about to replace the one on my boat. The one I have uses a spin on filter, but I'm going to sideways upgrade to one that also has a clear bowl, since I'm fighting some fueling issues at the moment.
In reply to Brett_Murphy (Agent of Chaos) :
I believe there should be one already on the engine itself. Under the cowl... maybe on the back starboard side? It looks kind of like a dryer you would put on your air hose with a little clear plastic bowl that screws on.
We went back out last weekend and what do you know - the motor runs much better when the vent is open on the fuel tank. We've had a ton of rain so the reservoir is quite flooded:
Yes, that's supposed to be a concrete dock that I can tie up to and it's completely underwater. I ended up walking the boat off the trailer and tying it to the lamp post, then doing it in reverse for retrieval. It was a beautiful day to be out on the water, hitting the low 50s and just sunny sunny sunny. We did some fishing but they fish had something else in mind. Check this out:
Just scads and scads of fish everywhere in the 20-30 foot deep range. Time after time we put lures and worms in there and they just ignored them. I think the water was just too cold, you can see on the finder it was 46 degrees. We got skunked, but we enjoyed a nice time on the water.
The red light on the motor still comes on at full throttle. I think Curtis has it exactly right that I need a different prop. My assumption is steeper pitch right? Factory is a 10" pitch, I assume a slight change is all that's called for you can get an 11" pitch and that might be my next step. I wish there was a cheaper way to try multiple props.
Oh, I mentioned the stiff steering in the last post: I removed the steering wheel and sure enough the plastic trim collar is interfering. For this day I just removed the collar and put the wheel back on. I'll figure out a way to get the interference cured.
Do you have a tach to determine your RPM at full throttle? How light was your load this time compared to usual? In the summer this might not be a problem as the motor is running in cool air and water and making more power than it will when those are hit.
In reply to dculberson :
Propeller pitch works the other way. You’ll need one with less pitch than the 10” you have now if you’re overloading the engine assuming that’s what the red light means. Going up to an 11” would reduce RPM. Agreed with Curtis and Sonic that you should try to get an accurate RPM reading with the engine at full throttle so you have a better idea of what’s going on.
Suzuki should have an RPM range listed in the engine manual and you want to select a propeller that will run in that range at the passenger and equipment load you typically run the boat with.
Edited to add: There are some very good propeller selection tools available online. If I’m looking at the correct information your engine has an operating RPM range of 4700 - 5700 RPM and a 2.08:1 gear ratio in the lower unit. Suzuki lists available propellers as low as 7” pitch. Your Starcraft should weigh about 870 pounds without gear from the iBoat link Mr Asa posted on page 1. I plugged all that into one of the calculators and you “should” be seeing around 16 MPH at full throttle with the 9” pitch. Does the manual say what the flashing red light means? It might be something other than the propeller pitch.
I can't imagine getting a light for over-loading an engine. I could see it for over-revving, but doubt that's the issue (it will hit a soft rev-limiter). You need a tach, even a digital tiny-tach is fine for picking props.
The manual will have descriptions for the lights.
The on-engine filters are not water separators. You want one mounted on the boat. The ones with the clear bowls are handy, but more expensive and they can swell and fail at the o-ring seal. The cheap automotive-style ones can be replaced often.
Water in the fuel will be the death of the engine.
11GTCS is spot on. Came here to say the same basic thing. If you K-swap a go-kart, you could have a final drive of 2.55 and it's great. If you K-swap a Suburban, you might need 5.10s. The confusing thing is that prop pitch is opposite. Higher numeric prop pitches are like lower numeric gears.
They supplied you with a prop that was expected to be put on something matched to a 10hp outboard, like a 120-lb aluminum vee or jon boat. Since you have it on a heavier boat, you might need a lower-pitched prop to make the RPMs spin to a point where the outboard is actually making 10 hp.
Many people think of boats like drag racers where you want the best acceleration with enough numeric final drive to not be too far below or above peak hp at the traps, but in reality they're more like a Bonneville land speed racer. If you gear it too tall, you'll hit aerodynamic drag that exceeds the hp becuase the RPM isn't high enough to make it's tested HP. If you go too short, you'll run out of RPM before your hp could overcome additional drag. You need a prop that allows the powerhead to spin at an RPM that is at or about max HP.
Long story short, find a way to test RPM.
11GTCS said:Edited to add: There are some very good propeller selection tools available online. If I’m looking at the correct information your engine has an operating RPM range of 4700 - 5700 RPM and a 2.08:1 gear ratio in the lower unit. Suzuki lists available propellers as low as 7” pitch. Your Starcraft should weigh about 870 pounds without gear from the iBoat link Mr Asa posted on page 1. I plugged all that into one of the calculators and you “should” be seeing around 16 MPH at full throttle with the 9” pitch. Does the manual say what the flashing red light means? It might be something other than the propeller pitch.
Yes, and he should be shooting for the middle to upper end of that range. This will mean the least loss of speed with a load of all the kids and an extra tank of gas.
I also think that 16 mph is optimistic with the Sport hull. It's not really a vee, it's actually more like a displacement flat bottom. The transition from vee to the flat bottom is abrupt, so those calculations don't really apply since the hull is pretty unique. Still, I think 12 mph is a possibility. If he had a 70-horse, it would apply since he would be fully on plane.
For reference, dad's pontoon can do 18 and change (gps) with two people and a 50hp Yamaha
Not sure if the red light is still an issue, but it looks like this motor has a low oil light and an over rev light
OVER-REVOLUTION CAUTION SYSTEM
This system is activated when engine speed exceeds the maximum recommended speed for
more than 10 seconds.
If this system activates, engine speed will automatically be reduced to approximately
3000 r/min. with the caution lamp lit.
This system must be reset by moving the throttle to the idle position for about one second to
restore full engine operation.
NOTICE
If the Over-Revolution Caution System activates at recommended maximum throttle and you are sure that the propeller pitch is sufficient and there are no factors like “over-trimming” or “ventilation”, there may be a problem with the Over-Revolution Caution System.
In reply to Curtis73 (Forum Supporter) :
Agreed that 16 MPH / on plane is optimistic with 9.9 HP, it probably doesn't have enough torque to push through the transition from displacement to planing. From what CJ posted the red light may actually be an over rev indicator, the propeller may be blowing out and cavitating. Small outboards pushing larger hulls often have 4 bladed propellers to spread the load out over more surface area. Need to be sure what the engine is doing first.
Another thing to keep in mind is that props are always under increasing load as RPMs go up.. Water can't compress, so pushing a boat forward is like driving uphill all the time, and the faster you want to go, the steeper the hill is.
I think that comparison/simile works correctly.
In reply to 11GTCS :
Good thought.
I don't want to fish back through all the pages... dculberson, do I recall you got the "big foot" or "high torque" version of the motor? If so, it may have a 4 blade prop and beefier bearings. They are often spec'd for pontoons or larger boats. If so, it's possible that it already has a lower pitch prop.
Brett_Murphy (Agent of Chaos) said:Another thing to keep in mind is that props are always under increasing load as RPMs go up.. Water can't compress, so pushing a boat forward is like driving uphill all the time, and the faster you want to go, the steeper the hill is.
I think that comparison/simile works correctly.
I think it works. I always likened it to aerodynamic drag but you're not only fighting air, but your headwinds get faster as the car goes faster.
Dude, thanks for all the input! I'll figure out a way to check the engine's RPM. I have a handheld digital tach but the proper Suzuki dash gauge is $400 and I'm not sure I'm that interested in knowing the RPMs. I think the flashing light is the over-rev warning, but again, the tach will have to be brought with me next time we're out so I can find out for sure.
I do not have the high thrust version of the motor.
Ok I finally got a chance to check the prop pitch of what's on there now. What's on there is a 4-blade 10" diameter 5" pitch which is apparently the stock prop for my specific motor. I think that's too low pitch for my boat. I also found a good deal on the Suzuki multifunction gauge and ordered that so I'll have a tach and diagnostic lights soon. But what I think is happening is the motor is over revving due to the low pitch prop and the rev limiter is kicking in. I'll wait until I know for sure but it looks like a steeper pitch prop is in my future. I might as well bundle that with the 20hp ecu. I mean, it just makes sense.
dculberson said:I might as well bundle that with the 20hp ecu. I mean, it just makes sense.
It really seems like the only reasonable thing to do.
5" pitch is super low, even for a pontoon or a large boat. If you put that thing on a 14' jon boat, it would try to spin at 8000. Not sure what Zuki was thinking.
I'm not sure if this translates to a boat not on plane, but the generally accepted standard is that one inch of pitch changes RPM by 150-200 rpms. If you're changing the number of blades, the rake of the cup, or changing brands, all bets are off. If you spring for a stainless prop, just know that they flex less than aluminum and therefore act like about 1" more pitch than a comparable aluminum... but again, all bets are off.
And yes. 20 hp ECU is a required investment. I'm making it mandatory on your behalf. :)
I received the multifunction tach and then the weather took a turn for the cold. I'll get it out this weekend instead. I also said, well, forget it and used the online prop calculators and ordered a prop. And an ECU. Maybe on-plane here we come?!
I got all the parts and when installing found the flame arrester requires a different gasket than the 9.9hp one. So I ordered that, hoping it would be here for this weekend, but it's "non-stock" so will have a 3-5 day shipping delay. Argh! Normally I'm very patient but I'm anxious to get the boat out with the new power!
If it makes you feel better, I'm anxious for you too. And jealous. I don't think I'll be on the water for at least another 2 weeks.
Flame arrester due today! And... saturday has rain and a birthday party for one of the kids school friends. But Sunday looks perfect. I'm hoping to make it out and try again for some crappie in Hoover reservoir.
Curtis73 (Forum Supporter) said:5" pitch is super low, even for a pontoon or a large boat. If you put that thing on a 14' jon boat, it would try to spin at 8000. Not sure what Zuki was thinking.
I'm guessing that most of them in this country are intended to be kickers, so they're pitched to move a 19'-23' boat at idle.
mtn said:Curtis73 (Forum Supporter) said:5" pitch is super low, even for a pontoon or a large boat. If you put that thing on a 14' jon boat, it would try to spin at 8000. Not sure what Zuki was thinking.
I'm guessing that most of them in this country are intended to be kickers, so they're pitched to move a 19'-23' boat at idle.
Most likely for moving a large sailboat at slow speeds. You need thrust, not speed to get all that displacement moving and stopped.
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